Enter these codes at the password screen.

HAROLDHAND -- All levels, all weapons, infinite ammunition, a "Get Out Of Jail Free" card, armor, parrot picture, 9,999,990 points, 99 lives, 5x multiplier, no cops, and display coordinates.
GETCARTER -- All levels, all weapons, infinite ammunition, "Get Out Of Jail Free" card, armor, 99 lives, 5x multiplier, maximum wanted level, display coordinates.
FREEMANS -- All levels, all weapons, infinite ammunition, "Get Out Of Jail Free" card, armor, 5x multiplier.
DONTMESS -- All weapons, infinite ammunition, "Get Out Of Jail Free" card, armor.
TOOLEDUP -- Same as above.
SORTED -- All levels, all weapons, infinite ammunition, "Get Out Of Jail Free" card, armor.
RAZZLE -- All levels.
READERWIFE -- Same as above.
MAYFAIR -- London levels 1-2.
PENTHOUSE -- London levels 1-3.
MCVICAR -- 99 Lives.
BIGBEN -- 9,999,990 points.
SIDEBURN -- 5x multiplier.
OLDBILL -- Max wanted level.
GRASS -- No cops.
SWEENEY -- Display coordinates.